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notro edited this page Aug 13, 2013 · 35 revisions

This is a step-by-step guide showing how to add and compile a new FBTFT driver in 30 minutes.
Note: This example driver doesn't follow the current preferred way to write FBTFT drivers.

This guide can also be used to get the latest driver update, if a new image hasn't been released yet. Follow the guide and skip the example driver.

If you want to contribute code, see Submitting patches

Boot with latest FBTFT image.

Expand root file system size.

sudo raspi-config
# expand_rootfs

Install dependencies

sudo apt-get update
sudo apt-get -y install git libncurses5-dev

Samba (optional)

Samba can be used to aid development on the Pi.

sudo apt-get -y install samba samba-common-bin

sudo cp /etc/samba/smb.conf /etc/samba/smb.conf.org


sudo sed -i '/ Share Definitions /q' /etc/samba/smb.conf

cat <<EOF | sudo tee -a /etc/samba/smb.conf

[homes]
   comment = Home Directories
   browseable = no
   read only = no
   create mask = 0644
   directory mask = 0755
   valid users = %S

EOF

sudo service samba restart
sudo smbpasswd -a pi

Home directory for user pi will be available at \\xxx.xxx.xxx.xxx\pi

Source

We don't need the complete git history (--depth 1). This will speed things up considerly.

cd
git clone --depth 1 git://github.com/raspberrypi/linux.git

fbtft source

cd ~/linux/drivers/video/
git clone https://github.com/notro/fbtft.git

# Let make/kbuild see the directory and config options.
echo "obj-y += fbtft/" >> Makefile
sed -i 's/endmenu/source "drivers\/video\/fbtft\/Kconfig"\n\nendmenu/' Kconfig

Preparation

cp ~/extra/.config ~/linux/
cp ~/extra/Module.symvers ~/linux/

cd ~/linux
make prepare scripts

Example driver: hellofb

This shows how to add a new driver.

Add to ~/linux/drivers/video/fbtft/Kconfig

config FB_HELLO
        tristate "Example FBTFT driver"
        depends on FB_TFT

Add to ~/linux/drivers/video/fbtft/Makefile

obj-$(CONFIG_FB_HELLO)           += hellofb.o

Add to static struct spi_board_info fbtft_device_spi_displays[] in file ~/linux/drivers/video/fbtft/fbtft_device.c

        }, {
                .modalias = "hellofb",
                .max_speed_hz = 32000000,
                .mode = SPI_MODE_0,
                .platform_data = &(struct fbtft_platform_data) {
                        .gpios = (const struct fbtft_gpio []) {
                                { "reset", 25 },
                                {},
                        },
                }

Create ~/linux/drivers/video/fbtft/hellofb.c

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/gpio.h>
#include <linux/spi/spi.h>
#include <linux/delay.h>

#include "fbtft.h"

#define DRVNAME	    "hellofb"
#define WIDTH       128
#define HEIGHT      160


/* Module Parameter: debug  (also available through sysfs) */
MODULE_PARM_DEBUG;


static int hellofb_init_display(struct fbtft_par *par)
{
	fbtft_dev_dbg(DEBUG_INIT_DISPLAY, par->info->device, "%s()\n", __func__);

	printk("Hello World");

	return 0;
}

struct fbtft_display hellofb_display = {
	.width = WIDTH,
	.height = HEIGHT,
};

static int hellofb_probe(struct spi_device *spi)
{
	struct fb_info *info;
	struct fbtft_par *par;
	int ret;

	fbtft_dev_dbg(DEBUG_DRIVER_INIT_FUNCTIONS, &spi->dev, "%s()\n", __func__);

	info = fbtft_framebuffer_alloc(&hellofb_display, &spi->dev);
	if (!info)
		return -ENOMEM;

	par = info->par;
	par->spi = spi;
	fbtft_debug_init(par);
	par->fbtftops.init_display = hellofb_init_display;

	ret = fbtft_register_framebuffer(info);
	if (ret < 0)
		goto out_release;

	return 0;

out_release:
	fbtft_framebuffer_release(info);

	return ret;
}

static int hellofb_remove(struct spi_device *spi)
{
	struct fb_info *info = spi_get_drvdata(spi);

	fbtft_dev_dbg(DEBUG_DRIVER_INIT_FUNCTIONS, &spi->dev, "%s()\n", __func__);

	if (info) {
		fbtft_unregister_framebuffer(info);
		fbtft_framebuffer_release(info);
	}

	return 0;
}

static struct spi_driver hellofb_driver = {
	.driver = {
		.name   = DRVNAME,
		.owner  = THIS_MODULE,
	},
	.probe  = hellofb_probe,
	.remove = hellofb_remove,
};

static int __init hellofb_init(void)
{
	fbtft_pr_debug("\n\n"DRVNAME": %s()\n", __func__);
	return spi_register_driver(&hellofb_driver);
}

static void __exit hellofb_exit(void)
{
	fbtft_pr_debug(DRVNAME": %s()\n", __func__);
	spi_unregister_driver(&hellofb_driver);
}

/* ------------------------------------------------------------------------- */

module_init(hellofb_init);
module_exit(hellofb_exit);

MODULE_DESCRIPTION("Example FBTFT driver");
MODULE_AUTHOR("Noralf Tronnes");
MODULE_LICENSE("GPL");

Configure

Start kernel configuration program

cd ~/linux
make menuconfig

Enable hellofb

Device Drivers  ---> Graphics support  --->  Support for small TFT LCD display modules  --->

<M>   Example FBTFT driver

make prepare

Build

This can be run from any directory

make -C /lib/modules/$(uname -r)/build SUBDIRS=drivers/video/fbtft modules

Test

sudo dmesg -C
sudo modprobe fbtft
sudo insmod ~/linux/drivers/video/fbtft/fbtft_device.ko name=hellofb
sudo insmod ~/linux/drivers/video/fbtft/hellofb.ko debug=3
dmesg

fbtft_device:  SPI devices registered:
fbtft_device:      spidev spi0.1 500kHz 8 bits mode=0x00
fbtft_device:  'fb' Platform devices registered:
fbtft_device:      bcm2708_fb id=-1 pdata? no
fbtft_device:  GPIOS used by 'hellofb':
fbtft_device:    'reset' = GPIO25
fbtft_device:  SPI devices registered:
fbtft_device:      spidev spi0.1 500kHz 8 bits mode=0x00
fbtft_device:      hellofb spi0.0 32000kHz 8 bits mode=0x00


hellofb: hellofb_init()
hellofb spi0.0: hellofb_probe()
hellofb spi0.0: fbtft_request_gpios: 'reset' = GPIO25
hellofb spi0.0: hellofb_init_display()
hellofb spi0.0: Elapsed time for display update:   16.561898 ms (fps: 60, lines=160)
graphics fb1: hellofb frame buffer, 40 KiB video memory, 4 KiB buffer memory, fps=20, spi0.0 at 32 MHz

sudo rmmod hellofb fbtft_device

Install

# install the new driver
sudo cp /lib/modules/$(uname -r)/build/drivers/video/fbtft/fbtft_device.ko /lib/modules/$(uname -r)/kernel/drivers/video/fbtft/
sudo cp /lib/modules/$(uname -r)/build/drivers/video/fbtft/hellofb.ko /lib/modules/$(uname -r)/kernel/drivers/video/fbtft/
sudo depmod

# update all drivers/modules
sudo cp -v /lib/modules/$(uname -r)/build/drivers/video/fbtft/*.ko /lib/modules/$(uname -r)/kernel/drivers/video/fbtft/
sudo depmod

sudo modprobe fbtft_device name=hellofb
sudo modprobe hellofb debug=3

Submitting patches

I you want me to include your driver, follow these rules:

  • The license the code is released under has to be GPL version 2 or later. Add this information at the top of the file.

  • Agree with the Developer's Certificate of Origin 1.1 (12. Sign your work)

  • Follow the Linux kernel coding style
    Use linux/scripts/checkpatch.pl --file fb_xxx.c to verify your code.
    Lines can exceed 80 columns if the meaning is hard to grasp when breaking up the line. Never exceed 132 columns.

  • Make an issue and include your driver in a code block for review.

  • When the driver is approved, I can just copy the code from the issue, or you can make a pull request with just one commit in it. If I commit the driver directly from the issue, a Signed-off-by line will be added to the commit message to credit the author.

Except for trivial patches, make an issue first before making a pull request too see if I agree with you. Only one fix/feature per commit and vice versa. I can commit simple changes directly from an issue, a pull request is not needed.

Kernel messages in SSH session

When doing development and testing from a SSH session, it's nice to see the that kernel panic message before everything freezes.

Make file /etc/rsyslog.d/kern_pi.conf with contents:

kern.err  pi

This will show kernel error messages and worse when user pi is logged in.

service rsyslog restart

piwik

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